The overall goal of this project is to define the function of the protein tyrosine phosphatase SHP-1 in viral infections of the CNS. SHP-1 is expressed at especially high levels in mature oligodendrocytes and in the CNS white matter of mice. Mice genetically deficient in SHP- I (motheaten and viable motheaten mice) have a dramatically increased susceptibility to the attenuated BeAn strain of Theiler's murine encephalomyelitis virus (TMEV) following intracerebral inoculation. These mice display numerous virus-infected cells in spinal cords, extensive demyelination and spastic limb paralysis, and greatly increased virus replication. In vitro, motheaten mouse oligodendrocytes infected with TMEV show increased cytopathic effects and virus replication and do not respond normally to the antiviral activities of IFN-J3. Taken together, it is proposed that rapid onset of demyelination in motheaten mice represents a defect in the interferon system in oligodendrocytes. Proposed studies are focused on determining the role of SHP- 1 in the appropriate induction of antiviral state genes by analyzing altered responses in motheaten relative to normal littermate cells. The specific aims are first to quantify replication and spread of TMEV in oligodendrocytes both in vitro and in the CNS of motheaten and normal littermate mice using standard virological techniques. Second, the altered expression and activity of antiviral state and pro-apoptotic genes in purified cultured oligodendrocytes from these mice will be determined using molecular approaches to detect protein and mRNA of these genes. Third, the mechanism by which SHP-l mediates interferon signaling in oligodendrocytes will be determined using techniques to analyze transcription factor activation. In this way, the role for SHP-l expression in oligodendrocytes in protecting against CNS virus infections will be characterized. It is proposed that SHP-1 plays an essential role in the mediating the actions of the interferons and virus-host interactions in the CNS.